Changes

===Digestive system===

===Digestive system===

[[Image:Ventral_neck_organs_rat.jpg|thumb|400px|Ventral neck organs in the rat <ref name="Boorman"/>.]]

[[Image:Ventral_neck_organs_rat.jpg|thumb|400px|'''Rat Incisors''' <br> Alexey Krasavin 2007, WikiMedia Commons]]

'''''Oral cavity:''''' The dental formula of the rat is 2(I 1/1; M 3/3).  Incisors are continuously erupting and are maintained at a constant length by attrition of occlusal surfaces.  This results in total renewal every 40-50 days.  Their yellow colour increases with age and is a result of iron containing pigments.

'''''Oral cavity:''''' The dental formula of the rat is 2(I 1/1; M 3/3).  Incisors are continuously erupting and are maintained at a constant length by attrition of occlusal surfaces.  This results in total renewal every 40-50 days.  Their yellow colour increases with age and is a result of iron containing pigments.